Since the fault dynamic of droop-controlled inverter is different from synchronous generators (SGs)

protection devices may become invalid

and the fault overcurrent may damage power electronic devices and threaten the safety of the microgrid. Therefore

it is imperative to conduct a comprehensive fault analysis of the inverter to guide the design of protection schemes. However

due to the complexity of droop control strategy

existing literatures have simplified asymmetric fault analysis of droop-controlled inverters to varying degrees. Therefore

accurate fault analysis of a droop-controlled inverter is needed. In this paper

by analyzing the control system

an accurate fault model is established. Based on this

a calculation method for instantaneous asymmetrical fault current is proposed. In addition

the current components and current characteristics are analyzed. It was determined that fault currents are affected by control loops

fault types

fault distance and nonlinear limiters. In particular

the influences of limiters on the fault model

fault current calculation and fault current characteristics were analyzed. Through detailed analysis

it was found that dynamics of the control loop cannot be ignored

the fault type and fault distance determine fault current level

and part of the limiters will totally change the fault current trend. Finally

calculation and experimental results verify the correctness of the proposed method.